What Greek letter is used to signify summation?

The story behind the answer

Sigma is correct because the uppercase Greek letter Σ is the standard symbol for summation, instructing you to add a sequence of terms. The others serve different roles: Δ (Delta) denotes change or difference, α (Alpha) often labels angles or coefficients, and Ω (Omega) can represent the last item, angular velocity, or asymptotic bounds in computer science.

Historically, the summation symbol was popularized by Leonhard Euler in the 18th century to compactly represent long sums. Memory tip: Sigma and Sum both start with “S,” and Σ looks like a stylized S turned angular—think “S for Sum.”